This proposal is part of a continuing effort to understand how the Drosophila embryo regulates the usages of its maternal-message. Two specific populations of message have been isolated as well as an enriched cDNA fraction for each that will be investigated in detail. The first one is the low-complexity fraction representing approximately 60 different sequences. The second fraction consists of the sequences present in the oocyte which disappear during development, approximately 33 different sequences. Cot-analysis will be performed to determine whether the sequences are transcribed from unique or repetitive genes. The sequences will also be mapped on polytene chromosomes by in situ -hybridization. The sequence complexity of the mRNA sequences that appear by gastrulation will be determined by Rot-analysis. Recombinant DNA clones are being constructed with Drosophila nuclear DNA. The enriched cDNA fractions will be used to identify those clones containing the genes for the low complexity and disappearing message sequences. These clones will then be characterized.